Design data for road tunnel ventilation have been constantly updated mainly due to steady tightening of emission laws for vehicles and changes in the risk assessment of a tunnel fire. In 1995, a new recommendation was issued by Permanent International Association of Road Congresses (PIARC) after reviewing the art of tunnel ventilation over the last 15 years. This recommendation needs to be considered in tunnel ventilation systems designed from then on. Not many tunnel ventilation systems have been designed based on this recommendation yet. From different ventilation systems applied to a tunnel, longitudinal ventilation system has its own superiority. Mean time, some limitations such as longitudinal air velocity, maximum pollution concentration and etc, exist in tunnels. These limit the length of a tunnel that can be ventilated longitudinally. Therefore, longitudinal ventilation systems need to be studied carefully for long tunnels in early design process. In present paper, ventilation capacity of a long tunnel is calculated based on PIARC 1995 recommendation. For this purpose, Carbon Monoxide is assumed to be the main polluting agent in tunnel air considering traffic combination. Aerodynamic characteristics and pollution concentrations along the tunnel are numerically simulated for different traffic speeds and rates to study longitudinal ventilation. A computer program based on transient flow model is used to simulate tunnel ventilation. The software used in this study permits account to be taken of the influence of jet fans, vehicle drag, emission rate, pollution, atmospheric pressure at tunnel portals and other physical characteristics of tunnel. Recommendations of Permanent International Association of Road Congresses are used in simulation process.
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